Automatic short-circuiting device



April 20, 1965 M- DEMARET 3,179,770

AUTOMATIC SHORT-CIRCUITING DEVICE Filed Jan. 10, 1963 2 Sheets-Sheet 1 April 20, 1965 M. DEMARET 3,179,770

AUTOMATIC SHORT-CIRCUITING DEVICE Filed Jan. 10, 1963 2 Sheets-Sheet 2 1 2b 2 ll /.9 2 I? l5 7 3 7 I I! L J I ll] I 78 a .22 24 23 76 United States Patent 4 Claims. in. zss iis It is an object of the present invention to provide an automatic device to short-circuit at least one of the ole ments of a circuit supplied by a leakage transformer, particularly at least one of the tubes of a luminous sign, the said device effecting a process using the increase of the supply voltage of an element, which results from the break in the circuit resulting from the failure of the said element, to cause the build-up of an are which acts on a thermo-sensitive element causing the said short-circuit.

Numerous devices are known which have two fixed contacts, one moving contact, a spring which i an electrical conductor and a thermo-sensitive element, inside an insulating sleath. Such devices may be connected in parallel with the terminals of the elements making up a circuit, so as to constitute automatic parts short-circuiting the said element in the case of failure.

With the help of these devices, as soon as one of the tubes of a luminous sign is extinguished, it is automatically placed out of the circuit, the result of which is to maintain the supply to the other tubes, which thus remain illuminated.

Finally, a resistance, equivalent to that of the corresponding tube, may be connected to such devices in accordance with prior art. The resistance is then mounted in series with the contacts shunt connected to the terminals of the said tube.

Such devices have a number of disadvantages: in particular, their working is hazardous, since, in certain cases, an excess voltage smaller than that due to the deterioration of a tube may cause the short-circuit of the latter, and, in other cases, they may stay blocked in the open position when they are attracted by an excess voltage for which they do not function, as they are sensitive to atmospheric conditions (temperature, humidity, corrosive agents, etc). Furthermore, such devices are relatively expensive to make and their use considerably increases the cost of a luminous sign.

The present invention has for an object to remedy the aforementioned and accordingly provides an automatic de vice for short-circuiting at least one of the elements of the circuit supplied by a leakage transformer, particularly at least one of the tubes of a luminous sign, comprising an electrically insulating sheath, two fixed contacts, a moving contact, an electrically conductive spring and a thermosensitive element all mounted within said sheath, said moving contact being mounted free to movewithin said insulating sheath and opposite one of said fixed contacts, the said moving contact being connected to the second of said two fixed contacts, both by said conductive spring which urges it against said first fixed contact, and by said thermo-sensitive element which is intended to keep it away from said first fixed contact so long as an arc does not build up between the latter and the said moving contact electrically connected through said spring to said first fixed contact.

Other characteristics and advantages of the invention will become apparent from the detailed description which follows, and in order that the invention may be more clearly understood, reference will now be made to the accompanying drawings, which show three embodiments thereof by way of non-limiting examples and in which-- lidi j'm Patented Apr. 20, 1965 ice , cated in an electrically insulating sheath exemplified as a glass tube 2 whose two ends 2a and 2b are secured to plugs 3. This device has conductive discs 4a and 4b applied, and maintained, against the plugs 3. The discs 4a and 4b comprise the fixed contacts hereinabove referred to, and are connected in circuit by the conductive wires 5a and 5b respectively. The disc 41) is also connected by a waxed thread 6 forming a loop, as shown, to another conductive disc 7. The disc 7 comprises the moving contact hereinabove referred to which is free to move inside the tube 2. The thread 6 normally keeps the disc 7 away from the fixed contact formed by the disc 4a. A spring 8, which is normally compressed, as in the position shown, is made of a material which is a conductor of electricity, the said spring remaining in constant contact with the disc 4Z7, but tending to urge the disc 7 towards the disc 4a.

The normal gap between the disc 7 and the disc 4a is such that an arc builds up between these two discs when there is a certain predetermined voltage between them. The build-up of the arc produces a spark which ignites the thread 6; the disc 7 is no longer held back and is brought into contact with the disc 4a by the action of the spring 8, this contact re-establishing the passage of the current, short-circuiting the element to whose terminals the device is connected.

In the schematic circuit diagram of FIGURE 2, a plurality of the devices of FIGURE 1 are shown at 1a, lb, 1c, 1d and 1e and are mounted in parallel with the terminals of five neon tubes 9a, 9b, 9c, S d and 9e, placed in series and supplied through a leakage transformer 14?. As is known, so long as the secondary coil of such a transformer has no load, the voltage between the secondary terminals ltla and 19b is very high. As soon as a current passes, however, this voltage is greatly reduced.

Thus, as soon as the current stops passing for any accidental reason, e.g., as a result of the failure of the tube $1), the voltage at the terminals of the device lb increases for two reasons.

Firstly, since each working tube acts as a (negative) resistance and the circuit is open, the total voltage existing between the terminals Ida and full), is present between the terminals of the device 1b placed in parallel with the failing tube 9b, the said voltage being normally distributed, during working, in proportion to the length of the various tubes 9a, 9]), l e, 9:! and 9e, it all the tubes 9 have the same characteristics.

Secondly, since the circuit is open, the secondary coil of the transformer is no longer loaded and the voltage between the terminal lilo and lid!) is considerably increased.

Thus, raising the voltage between the terminals of the device 1b, causes the build-up of an are which shortcircuits the tube 9b as explained above in connection with the device of FIGURE 1. However, the other tubes are still supplied and function normally.

Before the excitation of the tubes of the sign, these tubes, which are placed in series, and although they are very resistive, derive sufhcient current in relation to the circuit of the device, for the power necessary for the build-up of the are between the contacts of the device not to be reached between the said contacts.

The output of the transformer varies, depending on the characteristics of the tubes, such as tleir cross-section, the nature (neon, argon etc.) of the gases, the pressure at which the gases have been placed in the tubes, and the required light power. The gap between the contacts of the device may be determined accordingly.

It will be appreciated that the inflammable thread 6 may be replaced by any other textile or metal thread which may be broken by the action of the spark, and the glass tube by any other envelope made of an electrically insulating material which may, if desired, be covered.

Thus the circuit-breaking are which develops when the lighting tube to which the device is connected fails, must be located within the tubular insulating sheath 2, 3, to cause the closing of a switch.

In accordance with a second embodiment of the invention, shown in FIGURES 3 and 4, wherein like numerals refer to like parts of FIGURE 1, the switch under consideration has two fixed contacts 11 and 12 which are shunt-connected by the means already described, to the terminals of an associated lighting tube. Placing the said tube out of circuit results in an increase in the difference in potential between the terminals of the other tubes of the circuit. Should this impair the working of the installation, a resistor 13 may be provided, as shown in FIGURE 3, connected in series with one or other of the fixed contacts ill and 12. The characteristic of the resistor 13 is virtually equivalent to that of the tube connected to the device, so that placing the said tube out of circuit does not causes an increase in the difference in potential applied to the terminals of the other tubes, since the resistor 13 is connected in series with the latter through the switch. The resistor 13 may be independent of the device, but it may be more advantageous to incorporate it with the latter, and, to this end, the said resistor is inserted in the tubular sheath 2 between one of the end plugs 3 and an intermediate partition 14 integral with the sheath. In this case, the ends of the resistance are connected to the corresponding fixed contacts ill or 12 and to a connecting element 315. In this second embodiment, the fixed contact llZ, whether it is supported by a plug 3 (FIGURE 4) or by the partition 14 (FIGURE 3), is made up of a metal loop-shaped thread 16, the free end of this thread being crooked and stretching beyond the loop to form a projecting electrode point 17. In the example shown, the loop 316 is fiat and roughly triangular, but it will be appreciated that it may be circular (or a conical spiral) and central on the point 17.

The other fixed contact llll is made up of a metal cup 18 and a central stem 19, connected together by any appropriate means, such as a soldering 2h. The stem 19 may be supported either by the other plug 3, or by the partition 14, and it extends axially within the tubular sheath 2, so that its end constitues a second electrode point 21, arranged opposite the first point 117.

The cup 18 of the fixed contact fill has an approximately hemispherical shape. It co-operates with an identical cup 22 constituting the moving contact of the switch. These two cups are mounted opposite one another and enclose a spring 8 which is electrically conductive and which is inserted between the fixed contact 11 and the moving contact 22. This spring tends to push the moving contact 22 back so as to urge it against the fixed contact 12, but this can only happen when the tube connected to the device has broken down. So long as this tube works normally, the moving contact 22 must be kept near the fixed contact 11, against the action of the spring 8, but it must be so arranged that it no longer keeps this position as soon as an electric arc is built up between the electrode points 17 and 21. Moreover, the distance between the electrode points is so selected that an arc can only build up between them when the voltage which is applied to them is equal to the circuit-breaking excess voltage which develops when the tube fails.

To keep the moving contact 22 near the fixed contact ill, a fusible member 23 is used to connect the stem 19 of the said fixed contact to the cup of the said moving contact. In the example shown, the cup 22 has a hole 24 at its centre and this cup is threaded onto the electrode point 21, so that the fusible member 23 can take the form of a soldered joint between the point and the cup.

In the normal working condition the switch constituted by the device is open (FIGURE 3). At the exact moment when a failure of the lighting tube occurs, a breaking excess voltage occurs at the terminals of the tube, and also, as a result, between the electrode points 17 and 271. An arc builds up between these electrodes and this are causes the member 23 to melt, thus freeing the cup 22 which forms the moving contact. From this moment, the action of the spring 8 takes over and causes the projections of the said moving contact towards the fixed contact 12 until the cup 22 collides with the loop 16. In this position, the electrode point 17 passes through the hole 24 (FIGURE 4). This closing of the switch occurs very rapidly, so that the soldering forming the connection Z3 and adhering in its liquid state to the moving contact 22, does not solidify until the latter collides with the fixed contact 12. The solidified solder connects the two contacts intimately together and sets up a free connection between them. From this moment, the electrical circuit, which was broken before-hand as a result of the failure of the lighting tube, is closed once more through the fixed contact 11, the spring 8, the moving contact 22 and the fixed contact 12.

The invention is not limited to the embodiments illustrated and described in detail, as various modifications may be made to them without in any way departing from the scope of the invention.

I claim:

1. An automatic device, for short circuiting at least one element of an electric circuit, comprising:

(a) an electrically insulating sheath;

([2) a first fixed contact mounted on one end of said sheath;

(0) a second fixed contact mounted on the other end of said sheath substantially coaxially with said first fixed contact and having a free end directed towards said first fixed contact;

(d) a movable contact surrounding said second fixed contact and comprising a pair of separated elements, the first of said elements being electrically and mechanically joined to said second fixed contact near said other end of said sheath and the second of said elements being formed with a central longitudinal passage through which passes said free end of said second fixed contact;

(2) a compressed spring of electrically conductive material electrically and mechanically connected between said two elements of said movable contact for urging said second element towards said first fixed contact, and;

(f) a mass of solder soldered around said free end of said second fixed contact and to said second element on the surface thereof which faces said first fixed contact and in the region surrounding said longitudinal passage;

(g) whereby upon the creation of an are between said fixed contacts the portion of said solder mass adjacent said second fixed contact will be melted, thus removing the restraining force on said second element and permitting it to move into contact with said first fixed contact, carrying said solder mass with it, where the melted portion of said solder mass adheres to said first fixed contact, causing it to be soldered to said second element.

2. A device as recited in claim 1 wherein said two fixed contacts have identical cross-sectional shapes.

3. A device as recited in claim 2 wherein said two fixed contacts each have a cylindrical cross-sectional shape and said longitudinal passage has a cylindrical cross-section the diameter of which is slightly greater than that of said fixed contacts. a

4. A device as recited in claim 1 further comprising an impedance element whose impedance is identical with that of said at least one circuit element which said device is to short circuit said impedance element being connected 10 2,295,320

BERNARD A. GILHEANY, Primary Examiner.

in series with said first fixed contact.

References Cited by the Examiner UNITED STATES PATENTS Black 200-142 Beaulieu 200-142 Wall 200-142 Grifiin 200-142 Zeperski 200-142 Bourbon 200-142 Levenstein 200-118 Allen 200-118 

1. AN AUTOMATIC DEVICE, FOR SHORT CIRCUITING AT LEAST ONE ELEMENT OF AN ELECTRIC CIRCUIT, COMPRISING: (A) AN ELECTRICALLY INSULATING SHEATH; (B) A FIRST FIXED CONTACT MOUNTED ON ONE END OF SAID SHEATH; (C) A SECOND FIXED CONTACT MOUNTED ON THE OTHER END OF SAID SHEATH SUBSTANTIALLY COAXIALLY WITH SAID FIRST FIXED CONTACT AND HAVING A FREE END DIRECTED TOWARDS SAID FIRST FIXED CONTACT; (D) A MOVABLE CONTACT SURROUNDING SAID SECOND FIXED CONTACT AND COMPRISING A PAIR OF SEPARATED ELEMENTS, THE FIRST OF SAID ELEMENTS BEING ELECTRICALLY AND MECHANICALLY JOINED TO SAID SECOND FIXED CONTACT NEAR SAID OTHER END OF SAID SHEATH AND THE SECOND OF SAID ELEMENTS BEING FORMED WITH A CENTRAL LONGITUDINAL PASSAGE THROUGH WHICH PASSES SAID FREE END OF SAID SECOND FIXED CONTACT; (E) A COMPRESSED SPRING OF ELECTRICALLY CONDUCTIVE MATERIAL ELECTRICALLY AND MECHANICALLY CONNECTED BETWEEN SAID TWO ELEMENTS OF SAID MOVABLE CONTACT FOR URGNG SAID SECOND ELEMENT TOWARDS SAID FIRST FIXED CONTACT, AND; (F) A MASS OF SOLDER SOLDERED AROUND SAID FREE END OF SAID SECOND FIXED CONTACT AND TO SAID SECOND ELEMENT ON THE SURFACE THEREOF WHICH FACES SAID FIRST FIXED CONTACT AND IN THE REGION SURROUNDING SAID LONGITUDINAL PASSAGE; (G) WHEREBY UPON THE CREATION OF AN ARC BETWEEN SAID FIXED CONTACTS THE PORTION OF SAID SOLDER MASS ADJACENT SAID SECOND FIXED CONTACT WILL BE MELTED, THUS REMOVING THE RESTRAINING FORCE ON SAID SECOND ELEMENT AND PERMITTING IT TO MOVE INTO CONTACT WITH SAID FIRST FIXED CONTACT, CARRYING SAID SOLDER MASS WITH IT, WHERE THE MELTED PORTION OF SAID SOLDER MASS ADHERES TO SAID FIRST FIXED CONTACT, CAUSING IT TO BE SOLDERED TO SAID SECOND ELEMENT. 